Two law enforcement officials say Lanza saw himself as being in direct competition with Anders Breivik, the Norwegian man who killed 77 people in July 2011.
The sources say that Lanza wanted to top Breivik’s death toll, and the Sandy Hook Elementary School in Newtown, Connecticut was the “easiest target.”
Officials have not publicly revealed what led them to the motive, but sources say investigators have found evidence Lanza was obsessed with Breivik.
Lanza shot and killed 20 first graders and six adults at the school on December 14, 2012.
Unlike Breivik who surrendered, Lanza shot and killed himself as police closed in.